The present invention relates to a method for manufacturing food products by means of extrusion, to a device for performing such a method and to the obtained food products.
The general principle of producing foods by means of extrusion is already known in the prior art. It has become possible by means of extrusion to manufacture foods with a specific composition and shape at a relatively high production speed. Extrusion is particularly a much used method in the production of sausage.
A particular form of extrusion is so-called co-extrusion. The principle of co-extrusion in food products is described in, among others, Netherlands patent NL 6909339. This document describes the coating of a strand of food dough with a coating layer of collagen by means of co-extrusion. Following extrusion the coated strand is guided for strengthening purposes through a coagulation bath. Under the influence of the coagulation solution the collagen coagulates and/or precipitates and the coating layer is strengthened. A strand of food dough is thus formed which is at least partially coated with a strong coating layer of collagen.
In addition to proteins such as collagen, use is often also made in the food industry of polysaccharides, such as alginate, as coating agent for foods such as for instance sausage. The term alginate refers to a group of naturally occurring polysaccharides extracted from seaweed. In the presence of alkaline earth metals (such as, among others, magnesium and calcium) alginates can form gels relatively easily.
Studies have shown that the gelling of alginates under the influence of for instance calcium results due to the development of a three-dimensional structure. This is also referred to as the so-called egg-box model. When alginate is introduced into this three-dimensional structure, a relatively strong gel is created. Such a gel is highly suited to serve as coating layer of for instance a sausage.
In current practice a coating layer of alginate is often extruded onto a food dough strand in the making of sausage. The coating layer of the at least partly coated strand is then strengthened. This strengthening is done by guiding the extruded and coated strand through a salt bath containing calcium. Due to the presence of the calcium the coating agent (the alginate) will gel quickly and a strong coating layer forms on the food dough strand.
A drawback here however is that the coating agent undergoes rapid gelling on the outer surface such that calcium reaches the inner surface of the coating layer only with difficulty. In other words, due to the rapid gelling a gel layer forms on the outer surface of the coating layer which makes it difficult for sufficient calcium to permeate the coating layer. If insufficient calcium permeates the coating layer, a strong gel network resistant to the influence of sodium from the food dough strand does not form at the contact surface of the food dough and the coating layer. This may result in problems with shelf-life, texture and adhesion of the coating layer to the food dough strand. In order to solve this problem relatively high concentrations of calcium are generally used (from 10 to 15% by weight calcium salt). These high concentrations result in variations in taste, possibly a relatively high salt consumption, and corrosion of equipment.